The present invention relates to improved processes for the nickel catalyzed polymerization of olefins. These processes employ olefin feeds with very low carbon monoxide content (e.g., less than about 1 ppm, preferably less than about 0.1 ppm) such that the amount of carbon monoxide charged to the polymerization reactor is comparable to or less than the amount of nickel catalyst charged to the reactor.
Olefin polymers are used in a wide variety of products, from sheathing for wire and cable to film. Olefin polymers are used, for instance, in injection or compression molding applications, in extruded films or sheeting, as extrusion coatings on paper, for example photographic paper and digital recording paper, and the like. Improvements in catalysts have made it possible to better control polymerization processes and, thus, influence the properties of the bulk material. Increasingly, efforts are being made to tune the physical properties of plastics for lightness, strength, resistance to corrosion, permeability, optical properties, and the like, for particular uses. Chain length, polymer branching and functionality have a significant impact on the physical properties of the polymer. Accordingly, novel catalysts are constantly being sought in attempts to obtain a catalytic process for polymerizing olefins which permits more efficient and better-controlled polymerization of olefins.
Nickel catalysts for olefin polymerization have attracted interest based on their potential utility in generating polyolefins possessing novel microstructures and/or functionality. Both neutral and cationic nickel catalysts have been shown to be more tolerant of polar comonomers or additives than Group 4-6 transition metal catalysts for olefin polymerization (Ittel et al., Chem. Rev. 2000, 100, 1169). Neutral nickel catalysts have been shown to effect aqueous emulsion polymerizations (Claverie et al., Macromolecules (2001), 34(7), 2022-2026) and to copolymerize ethylene with functional monomers (Grubbs et al., Science (2000), 287(5452), 460-462). So-called xe2x80x9cnaked nickelxe2x80x9d cationic complexes have been shown to copolymerize norbornene with functionalized norbornene derivatives (Goodall et al., WO 98/56837). With cationic nickel complexes of bidentate N,N-donor ligands, ethylene has been copolymerized with ethyl undecenoate (Mackenzie et al., WO 99/62968), and polymerizations have been carried out in supercritical carbon dioxide (Brookhart et al., U.S. Pat. No. 5,866,663) and in the presence of millimolar concentrations of 2,6-di-tert-butyl-4-methylphenol (Mackenzie et al., U.S. Provisional Patent Application 60/298,893, filed Jun. 19th, 2001). In a related vein, it has also been reported that nickel catalyzed ethylene/carbon monoxide alternating copolymerizations proceed in super-critical carbon dioxide (Klaui et al., Angew. Chem., Int. Ed., (2000), 39(21), 3894-3896).
I have discovered that certain high activity nickel catalysts for olefin polymerization are extremely sensitive to the presence of carbon monoxide and are deactivated by stoichiometric amounts under olefin polymerization conditions. In view of the above cited references which suggest that nickel catalysts are more tolerant of polar comonomers and additives than existing commercial olefin polymerization catalysts, it is surprising and unexpected that such high sensitivities to carbon monoxide should be observed.
I have also found that by reducing the carbon monoxide content of the ethylene, significant improvements in catalyst productivity are observed at low catalyst loadings. Methods for reducing the carbon monoxide content of olefin feed streams are known (Rosenfeld, WO 95/21146). Such methods can be used in the present invention. The ability to achieve higher productivities simply by scrubbing the olefin feed to lower the carbon monoxide content is expected to be useful in achieving better economies in nickel-catalyzed polyolefin production. In the case of neutral nickel catalysts, including those comprising a bidentate N,N-, N,O-, or P,O-donor ligand, those catalysts which give very high activities for olefin polymerization (e.g., greater than about 50 kg polyolefin/g Ni/h) are also expected to be inhibited by carbon monoxide, since the rate of olefin/carbon monoxide copolymerization with such catalysts is likely to be lower than the rate of olefin polymerization. In general, more electrophilic neutral nickel complexes are expected to be more sensitive to inhibition by carbon monoxide than less electrophilic complexes.
In addition to the need to lower the carbon monoxide content in the olefin feed, with very low amounts of catalyst, it may also be necessary in some cases to lower the carbon monoxide content of the hydrogen which is added to control molecular weight. In the case of solution or slurry polymerization processes, it is similarly important that the solvent be low in carbon monoxide, and also low in diene (which can also inhibit the catalyst).
Thus, in a first aspect, this invention relates to a process for the polymerization of olefins, comprising contacting ethylene and optionally one or more alpha-olefins with a catalyst comprising a cationic nickel complex of a bidentate N,N-donor ligand, in the presence of less than about 1 equivalent of carbon monoxide per equivalent of nickel. In a first preferred embodiment, the process is carried out in the presence of less than about 0.5 equivalent of carbon monoxide per equivalent of nickel. In a second preferred embodiment, the process is carried out in the presence of less than about 0.25 equivalent of carbon monoxide per equivalent of nickel.
In a second aspect, this invention relates to a process for the polymerization of olefins, comprising contacting ethylene and optionally one or more alpha-olefins with a catalyst comprising a cationic nickel complex of a bidentate N,N-donor ligand, wherein the ethylene contains less than about 1 ppm carbon monoxide, the total pressure is greater than about 689 kPag (100 psig), wherein kPag refers to kiloPascals gauge pressure, and the temperature is greater than about 60xc2x0 C. In a first preferred embodiment of this second aspect, the ethylene contains less than about 0.5 ppm carbon monoxide, the total pressure is greater than about 689 kPag (100 psig), and the temperature is greater than about 70xc2x0 C.
In a third aspect, this invention relates to a process for the polymerization of olefins, comprising contacting ethylene and optionally one or more alpha-olefins with a catalyst comprising a neutral nickel complex of a bidentate N,N-, N,O-, or P,O-donor ligand, in the presence of less than about 1 equivalent of carbon monoxide per equivalent of nickel. In a first preferred embodiment of this third aspect, the process is carried out in the presence of less than about 0.5 equivalent of carbon monoxide per equivalent of nickel. In a second preferred embodiment, the process is carried out in the presence of less than about 0.25 equivalent of carbon monoxide per equivalent of nickel.
In a fourth aspect, this invention relates to a process for the polymerization of olefins, comprising contacting ethylene and optionally one or more alpha-olefins with a catalyst comprising a neutral nickel complex of a bidentate N,N-, N,O-, or P,O-donor ligand, wherein the ethylene contains less than about 1 ppm carbon monoxide, the total pressure is greater than about 689 kPag (100 psig), and the temperature is greater than about 60xc2x0 C. In a first preferred embodiment of this fourth aspect, the ethylene contains less than about 0.5 ppm carbon monoxide, the total pressure is greater than about 689 kPag (100 psig), and the temperature is greater than about 70xc2x0 C.